1. Field of the Invention
The present invention relates to an apparatus and method for purifying the oxidizing gas in a fuel cell that is used to generate electricity.
2. Description of the Related Art
A fuel cell generates electricity by causing an electrochemical reaction between a fuel gas and an oxidizing gas. Hydrogen is generally used as the fuel gas and air is generally used as the oxidizing gas. A noble metal such as platinum is generally used as the catalyst to cause an electrochemical reaction between the fuel gas and the oxidizing gas.
The air used as the oxidizing gas sometimes contains gas components (impurities) such as sulfur compounds and nitrogen oxides. When a catalyst made of platinum or other noble metal comes into contact with the impurities, its activity is reduced. If air used as the oxidizing gas is sent to the fuel cell without removing such impurities, the activity of the catalyst is reduced, which weakens the electrochemical reaction to cause a decrease in generated voltage. For this reason, an adsorbent (chemical filter) is provided in a fuel cell system for the purpose of removing impurities from the air. A carbon-based activated fiber or the like is generally used as the adsorbent, which adsorbs gas components such as sulfur compounds or nitrogen oxides. The adsorbent also releases the adsorbed gas components when heated to at least a certain temperature. Thus, by heating the adsorbent before it reaches the saturation adsorption amount, it is possible to maintain the adsorption capacity over a long period of time.
In conventional fuel cell systems, an electrical heater was provided for the thermal regeneration of the adsorbent, as described in, for example, Japanese Patent Application Publication No. JP-A-2005-129494 and Japanese Patent Application Publication No. JP-A-2004-327429.
When a fuel cell is installed on board a vehicle, however, there is limited space for installation, so that it is desirable to have a fuel cell system that uses fewer parts.